Archimedes' screw helps optimize fish catching, welfare and product quality

Abstract

Efficient fish handling during pre-slaughter is essential to ensure both animal welfare and product quality. However, the effects of different mechanized catching systems, such as Archimedes screws and vacuum pumps, on stress and flesh characteristics in farmed fish remain insufficiently understood. This study evaluated the physiological and quality-related impacts of three methods, manual netting (N), Archimedes' screw (A), and vacuum pump (V), on rainbow trout (Oncorhynchus mykiss) under two water temperatures: 10 °C (winter) and 17 °C (summer). A total of 240 fish were sampled and analyzed for plasma stress indicators (cortisol, glucose, lactate, triglycerides, non-esterified fatty acids, lactate dehydrogenase and creatine phosphokinase-CPK enzymes), muscle and liver enzyme activities, skin and liver color, fillet color at 0 and 24 h post-mortem, pH, and rigor mortis. Compared to the vacuum pump, the Archimedes screw significantly reduced stress responses (e.g., lower cortisol, lactate, and CPK), improved fillet appearance (higher L* at 24 h), and preserved muscle enzyme activity, particularly in summer. In contrast, fish caught with the vacuum pump showed greater metabolic disruption, reduced acetylcholinesterase activity, and more variable tissue coloration. However, under colder conditions, the screw's higher physical demands led to increased energy expenditure and stress indicators. Overall, results suggest that the Archimedes screw is a more fish-friendly mechanized method than the vacuum pump, offering better outcomes for welfare and product quality, especially when used at optimal water temperatures for the species